1. Field of the Invention
The present invention relates to a lithographic apparatus and a method for manufacturing a device.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs) An example of such an integrated circuit is a CMOS image sensor or a charge-coupled device (CCD) image sensor. In the manufacturing of those devices, a patterning device, which may be alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC or image sensor. This pattern can be transferred onto a target portion (e.g. including part of one or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam having a rectangular shape in a given direction (the “scanning” direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. In order to obtain a uniform illumination of the pattern the lithography apparatus includes a multi lens array. The multi lens array equalizes the intensity distribution in the illumination beam.
The intra-dose uniformity IDU is defined as
  IDU  =                    3        ⁢        σ            M        ⁢    100    ⁢    %  wherein σ represents the standard deviation of the measuring intensities, and M represents the average of the measured intensities in the rectangle shape illuminated by the slit. In case CMOS sensors or CCD sensor are manufactured with the aid of the known lithographic projection very tight restrictions are necessary of the intra-field dose uniformity, because small variations in the intra-field dose may cause undesired variations in the captured image of the CMOS sensor or CCD sensor.